1. Field of the Invention
The present invention relates to a liquid crystal display device used as a display part of an information equipment or the like and a method of manufacturing the same, and particularly to a transreflective type liquid crystal display device used for a low power consumption equipment such as a portable information terminal and a method of manufacturing the same.
2. Description of the Related Art
In recent years, an active matrix type liquid crystal display device including a thin film transistor (TFT) in each pixel has been widely used as a display device for any use. The liquid crystal display device is classified into a transmission type, a reflection type and a transreflective type by its lighting system. In the transmission type, transmitted light from a backlight unit is used for display. In the reflection type, reflected light of outside light is used for display. In the transreflective type, transmitted light of a backlight unit is used for display in a dark place and reflected light of outside light is used for display in a bright place. In recent years, as a display device for a mobile terminal or a notebook PC, a transreflective type (reflective and transmissive) liquid crystal display device in which display in both reflective and transmissive modes is enabled has been used.
Here, a conventional liquid crystal display device will be described. FIG. 74 shows a sectional structure of a reflection type liquid crystal display device disclosed in non-patent document 1 (set forth below). As shown in FIG. 74, a liquid crystal 106 is sealed between a pair of substrates 102 and 104 disposed to be opposite to each other. The alignment state of the liquid crystal 106 is a bend alignment called ROCB (Reflective Optically Compensated Birefringence). A reflecting electrode 116 having a mirror-like flat reflecting surface is formed on the surface of the one substrate 102 at the side of the liquid crystal 106. A common electrode 142 made of a transparent electrode film is formed on the surface of the other substrate 104 at the side of the liquid crystal 106. A phase difference film (quarter-wave plate) 120, a polarizing plate 122 and an optical path control film 124 are disposed in this order at the panel outer side (observer side) of the other substrate 104.
The optical path of incident outside light is bent by the optical path control film 124, reaches the reflecting electrode 116, is reflected, and is emitted toward the observer side. Since the optical path control film 124 for diffusing and transmitting light is provided, the optical path of the light reflected at the surface of the optical path control film 124 is different from the optical path of the light having been transmitted through the optical path control film 124 and reflected at the surface of the reflecting electrode 116. Then, when the observer sees the display screen, the display and the outside light do not overlap with each other, and a clear display image can be observed.
FIGS. 75A and 75B show a structure of a transreflective type liquid crystal display device disclosed in non-patent document 2 (set forth below). FIG. 75A shows a structure of approximately one pixel of the transreflective type liquid crystal display device, and FIG. 75B shows a sectional structure of the transreflective type liquid crystal display device cut along line X-X of FIG. 75A. As shown in FIGS. 75A and 75B, a pixel area is divided into a transmission area T and a reflection area R. An insulating material (resin layer) 130 is formed in the reflection area R of a TFT substrate 102 so that the cell thickness of the reflection area R becomes half of that of the transmission area T. A reflecting electrode 116 having an uneven surface is formed on the insulator 130. A protrusion 132 for alignment controlling a vertically aligned liquid crystal 106 is formed at the center part of the transmission area T of an opposite substrate 104. A pair of quarter-wave plates 120 are respectively disposed at the panel outer side of the TFT substrate 102 and at the panel outer side of the opposite substrate 104. A pair of polarizing plates 122 are respectively disposed at the further outer sides of the respective quarter-wave plates 120.
Although this liquid crystal display device is the same as the liquid crystal display device shown in FIG. 74 in that the reflecting electrode 116 is formed on the surface of the substrate 102 at the side of the liquid crystal 106, the reflecting surface of the reflecting electrode 116 is uneven. The incident outside light from the observer side is scattered and reflected at the reflecting electrode 116, and is emitted toward the observer side.
FIG. 76A shows a state in which a voltage is not applied to the liquid crystal 106, and FIG. 76B shows a state where a predetermined voltage is applied to the liquid crystal 106. As shown in FIG. 76A, in the state of voltage non-application, since a liquid crystal molecule is aligned vertically to the substrate surface, the liquid crystal 106 does not exert an optical effect on light. When a reflective display is performed, the light having been transmitted through the polarizing plate 122 is transmitted through the quarter-wave plate 120 and is incident on the liquid crystal 106, and after the light is reflected at the reflecting electrode 116, it is again transmitted through the quarter-wave plate 120. That is, the light is transmitted through the quarter-wave plate 120 twice, so that its-polarization state is rotated by 90°. Accordingly, this light is absorbed by the polarizing plate 122. Thus, black is displayed in the reflection mode.
Besides, when a transmissive display is performed, light having been transmitted through the polarizing plate 122 at the side of a backlight unit 188 is transmitted through the quarter-wave plate 120, is incident on the liquid crystal 106, and is transmitted through the quarter-wave plate 120 at the observer side. That is, the light is transmitted through the quarter-wave plate 120 twice, so that its polarization state is rotated by 90°. Accordingly, this light is absorbed by the polarizing plate 122 at the observer side. Thus, black is displayed in the transmission mode.
On the other hand, in the state where the predetermined voltage is applied, since the liquid crystal molecule is inclined with respect to the substrate surface, the liquid crystal 106 exerts a predetermined optical effect on light. As shown in FIG. 76B, light having been transmitted through the polarizing plate 122 changes its polarization state by the liquid crystal 106. Thus, white is displayed in both the reflection and transmission modes.
[Patent Document 1] JP-A-2000-56326
[Patent Document 2] JP-A-2000-171789
[Patent Document 3] JP-A-2002-202511
[Patent Document 4] JP-A-6-175126
[Patent Document 5] JP-A-7-311383
[Patent Document 6] JP-A-11-281972
[Patent Document 7] JP-A-2000-47251
[Non-patent Document 1] Uchida et al. “A Bright Reflective LCD Using Optically Compensated Birefringence Cell with Gray-Scale Capability and Fast Response”, SID 96 DIGEST, p. 618-621
[Non-patent Document 2] Jisaki et al. “Development of Transflective LCD for High Contrast and Wide Viewing angle by Using Homeotropic Alignment”, Asia Display/IDW '01, p. 133
In the structure of the reflection type liquid crystal display device as shown in FIG. 74, a use in combination with the transmission type has not been realized. This is because in the reflection type, on the premise that the light is transmitted through the liquid crystal 106 twice, the alignment state of the liquid crystal 106 is a hybrid alignment. In the hybrid alignment, there is a problem that birefringence is small when it is used in the transmission type, and a sufficient white display can not be performed. Besides, when it is used in the transmission type, there is a problem that viewing angle characteristics are low.
On the other hand, in the transreflective type liquid crystal display device shown in FIGS. 75A to 76B, it is proposed that the surface of the reflecting electrode 116 is formed to be uneven. However, in order to manufacture the transreflective type liquid crystal display device having the uneven reflecting electrode 116, in addition to a manufacture process of a normal transmission type liquid crystal display device, a process, such as formation and patterning of a resin layer and formation of the reflecting electrode 116, is further required. Thus, there arises a problem that the manufacture cost of the liquid crystal display device is raised.